2. How Stars are Really Named

In this section, I’ll give a brief review of the types of names which astronomers give to stars, and how they originated.

2.1. Constellations

Astronomers divide the sky into 88 constellations, or star patterns. Many of these patterns originated thousands of years ago, and had deep significance within the cultures and mythologies of various early civilisations – particularly that of the Greeks of around 2500 years ago. Others are much more recent inventions, dating only from the 17th and 18th Centuries AD. During this era, European explorers who travelled to the Southern Hemisphere invented new constellations in the region of the sky around the South Celestial Pole, which is never visible from Europe, and had therefore never before been mapped. Other people formed new constellations in the sky’s Northern Hemisphere, formed out of faint stars, simply to “fill in the gaps” between the traditional constellations.
Today, of course, constellations have no scientific significance whatsoever – but astronomers still use them, simply as a “convenient” ( in some cases, that’s a matter of opinion! ) means of dividing the sky into manageable regions, and of describing the locations of astronomical objects. Prior to the 20th Century, there was no “official” list of constellations, and many variations were in use – but in 1933, their names and boundaries were standardised by the International Astronomical Union. Rather awkwardly, their official names are in Latin – though of course, they all have “common” names in English and other modern languages.
Constellations really have nothing to do with the subject of this essay; I mention them here, simply because many stars have names derived from their parent constellations.

2.2. Traditional star names

Many of the brighter stars – those which make up the traditional constellation figures – have traditional “proper names”, which date back many centuries. Most of these are derived from Arabic, and were assigned by Arab astronomers around 1000 years ago – though a few are even older, and originate from classical Greek or Latin. Some of these names are pretty obscure, while others are well-known and still in common usage today – though really for no other reason than that they represent centuries of tradition.
A few of these traditional names, such as Sirius and Vega, are easy to remember, and actually quite convenient; it’s easier to say “Sirius” than “Alpha Canis Majoris”! Others are pretty awful, such as Deneb al Giedi and Zubenelgenubi, and are rarely used. Most of the Arabic names are in fact contractions of longer phrases, which were originally simply descriptions of the stars’ positions in the constellation figures, such as “Under the southern horn of the Bull” – so though these names sound exotic, they actually translate to something quite mundane!
Obviously, for anyone to claim to “rename” stars whose traditional names date back 1000 years or more, would simply be ludicrous. The star naming companies don’t try to do any such thing; they assign names to much fainter stars, which don’t have any recognised names – which means stars which are not visible to the naked eye. A consequence of this to astronomers will be discussed in Section 5.

2.3. Bayer letters and Flamsteed numbers

The first attempt to designate stars in a logical manner was made by Johann Bayer, who published a famous star atlas, the Uranometria, in 1603. Within each constellation, he assigned a Greek letter to each of the stars making up the constellation pattern. Often, though not always, he assigned these letters roughly in order of brightness, calling the brightest star Alpha, the next brightest Beta, and so on. Each star is identified by its Greek letter and the genitive form of its constellation’s name; thus the brightest star in Taurus is called Alpha Tauri, or “Alpha of Taurus”, the second brightest is Beta Tauri, etc.
This system has an obvious limitation; the Greek alphabet has only 24 letters, so you can only name 24 stars per constellation. Early in the 18th Century, John Flamsteed, Britain’s first Astronomer Royal, introduced another naming system, which used numbers instead of letters, so its use was unlimited. Again, stars were numbered within each constellation, with a star being referred to by its number and the genitive of the constellation. Instead of ordering the stars by brightness, Flamsteed ordered them by position; he allocated the numbers within each constellation in order of right ascension ( the celestial equivalent of longitude ). He assigned a number to virtually every naked-eye star in the sky – about 6000 of them.
Both of these systems came into common usage. The IAU has never established any “official” rules for naming stars – though it does so for other types of astronomical objects – or declared that any particular system should be used in preference to any other. The Bayer and Flamsteed systems are simply used as a result of long tradition and general agreement, and the IAU sees no need to do otherwise.
When we also consider the traditional “proper” names, some stars are now known by three different names; for example, Alpha Orionis, 58 Orionis and Betelgeuse are all one and the same. The convention on modern day star atlases is to use Bayer’s Greek letters for those stars which have them, and Flamsteed numbers for the remainder. There is also a completely separate system for naming variable stars, which uses pairs of Roman letters instead of Greek, and then numbers prefixed by V – such as V335 Orionis – after we run out of letters.
You may think that the above is pretty confusing – and it is! The system is admittedly a long way short of ideal – but it’s a legacy of astronomy’s long and rich history.

2.4. Catalogue numbers

The Bayer and Flamsteed systems assign names to the 6000 or so stars which are visible to the naked eye. For the millions of fainter stars, there are no names as such; astronomers refer to them by their numbers in various catalogues. Many different catalogues have been compiled since that of Flamsteed; some of these list every star in the sky down to a specified magnitude ( brightness ), while others list only stars of some specific type, or those which share a particular characteristic, and were compiled for someone’s specific research purposes. Some of these catalogues have come into widespread use, as a convenient means of identifying stars which have no other designation.
Depending upon which catalogue they are listed in ( and one star may be listed in several ), stars are referred to by their catalogue numbers, preceded by a catalogue designator, which is either its author’s name or a set of identifying letters. Thus we have such designations as Lalande 21185 and HD209458 ( these two are among the nearby stars now known to have planetary systems ). In the latter, HD indicates the Henry Draper Catalogue, published at Harvard University in 1924, which is probably the one most widely used for identifying stars; it lists the positions and spectral types of over 359000 stars. ( Confusingly, this was not compiled by the astronomer Henry Draper - in fact, it was compiled 40 years after his death – but it completed a process of classifying stars by their spectra, which Draper had begun, and so was named in his memory. ) Another well-known catalogue is that compiled by the Smithsonian Astrophysical Observatory in 1966; it lists 259000 stars, with numbers prefixed by SAO.
Older catalogues simply use sequential numbers, assigned in some logical order – e.g. in the Henry Draper Catalogue, stars are listed in order of right ascension – but more modern ones use numbers which correspond to the stars’ positions in right ascension and declination ( the coordinates used to identify an object’s location in the sky, equivalent to longitude and latitude respectively ), so that you can immediately find where a given star is in the sky, just by looking at its number.
The most comprehensive star catalogue so far is the Guide Star Catalogue ( GSC ), produced for the purpose of guiding the Hubble Space Telescope. This contains no less than 16 million stars.
It’s these stars – those which have no designation other than catalogue numbers – which are “named” by the star naming companies. The International Star Registry now specifically uses stars from the Guide Star Catalogue, so that each one so “named” can be unambiguously identified by its GSC number – though I don’t know what criteria the company used in its early days, before the GSC existed!

2.5. Human names

For the sake of completeness, I should mention here that there are a handful of stars which astronomers do refer to informally by human names, such as Barnard’s Star. These are well-known stars which are unusual or remarkable in some way, and are named in honour of the astronomers who discovered, or drew attention to, their unusual properties. These names are in no way “official”, but are widely used as a convenience.

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